The present invention relates to a method of preparing orthotrifluoromethyl aniline from trifluoromethyl benzene. Orthotrifluoromethyl aniline is industrially important because it is used as an intermediate in the synthesis of dyestuffs.
Kemichi Fukui et al. (Chemical Abstracts 1960 4430 b) describe the nitration of trifluoromethyl benzene to obtain metanitrotrifluoromethyl benzene, which is converted into metatrifluoromethyl aniline. The acetylation of the aniline compound by acetic acid gives metaacetylaminotrifluoromethyl benzene, the nitration of which yields 2-nitro-5-acetyl-aminotrifluoromethyl benzene.
The latter, by hydrolysis, gives 2-nitro-5-amino-trifluoromethyl benzene. The elimination of the amine group is effected by reductive diazotation, which makes it possible to obtain orthonitrotrifluoromethyl benzene, the reduction of which leads to orthotrifluoromethyl aniline.
The main drawback of this method is its length. Seven steps (not including separation and purification steps) are necessary to obtain the desired product from the trifluoromethyl benzene starting material. Furthermore, as is well known, diazotation is a difficult procedure. In addition, purification operations are necessary after most of the steps. Finally, yields are limited.
L. M. Yagupolsky and N. I. Manko (Chemical Abstracts 1954 8194 e) disclose treating orthotrifluoromethyl benzamide with sodium hypobromite in accordance with the Hoffman degradation reaction. One drawback of this reaction is the well known possibility of forming N-bromoamines, which are explosive. Furthermore, the raw material used in this process is not readily available industrially.